This invention relates to a method and to an electro-mechanical device for locking mobile cargo-containers for the purpose of reducing loss of container contents by theft. Such containers can be, but are not limited to: air, sea, and rail cargo containers; truck trailers; vans; rail cars; freight compartments on passenger buses; and the like.
Existing methods of locking cargo containers are generally confined to use of purely mechanical devices, the most common being the conventional key-operated padlock. Other lesser used means include: key-operated mechanical cross-bar locks; conventional mechanical combination padlocks; etc. In some select cases of transport of high value or sensitive cargos, carriers have resorted to welding the container doors shut as a deterrent to theft while the cargo is in transit.
As a supplement to mechanical locking devices, the security industry at times employs self-contained electrical alarm devices to announce unauthorized entry into cargo containers by producing audible siren or bell sounds as a deterrent to theft.
The primary disadvantage to using conventional key or combination operated mechanical locks resides in the difficulty of maintaining limited-access control of the key or combination for such devices. Also it is usually impossible or very difficult to change or alter the key or combination mechanisms when the security control of the key or combination is breached. Once the key is copied or duplicated, or the combination known to unauthorized personnel, the useful life of such device for security purposes is terminated, usually resulting in replacement of such device.
The disadvantage of supplemental electrical alarm devices is that they require a constant electric power source, usually a large battery with sufficient power to drive the alarm annunciator to indicate forced or unauthorized entry to the cargo container. Batteries mounted on the exterior of the cargo container are relatively easy to disconnect or defeat as a means of disarming the alarm, and are further subject to premature failure from extreme temperature variations. Batteries mounted and locked within the cargo compartment may, when exhausted or defective, leak corrosive battery acid which could damage the cargo contents or alarm device.
Prior attempts to develop electro-mechanical locks for mobile cargo-containers have produced devices that proved unreliable or impractical when subjected to the extreme environments and operations encountered in the freight transporting industry. Normally encountered conditions are: extreme temperature and weather variables; heavy shock and vibrations; steam cleaning of the containers; and rough handling of the container interior and exterior while loading and unloading cargo. Exposed interconnecting cables for electrical devices, on either interior or exterior, have proved to be particularly vulnerable to damage from such environments.
Known versions of re-settable electronic combination locks are readily available for use in "fixed" residential, commercial, and industrial installations, but as presently configured are not practical for use as mobile cargo-container locks. Such systems are generally installed in a building subject to minimal environmental changes and are usually coupled to the electrical power source used in the building capable of high electric power demands normally required by conventional electro-mechanical locking solenoids, or audio and visual alarm annunciators. Exposed electrical wiring is generally utilized within the locked room or area to interconnect the lock circuitry to a fixed electric power source, and to the locking solenoid and remote alarm annunciators. The circuits for such electronic combination locks are well known in the art as exemplified by U.S. Pat. No. 3,321,673. That patent utilizes well known techniques of arranging bistable latching multivibrators, or flip-flop stages, in series connection, whereby each preceeding multivibrator stage must be actuated by entry of a keyboard switch signal in a preselected sequence before the succeeding multivibrator will accept the next actuating signal, a pre-determined number of such steps in proper, and re-settable, sequence being necessary to energize and unlatch the lock mechanism.